The present invention relates to a neural stimulation systems, e.g., a spinal cord stimulation system. More particularly, the invention relates to neural stimulation leads that include lead fixation means, i.e., ways to assure that the lead, once implanted, does not move away from its desired implant location.
Spinal cord stimulation (SOS) is a well accepted clinical method for reducing pain in certain populations of patients. SCS systems typically include an implanted pulse generator, lead wires, and electrodes connected to the lead wires. The pulse generator generates electrical pulses that are delivered to the dorsal column fibers within the spinal cord through the electrodes which are implanted along the dura of the spinal cord. In a typical situation, the attached lead wires exit the spinal cord and are tunneled around the torso of the patient to a sub-cutaneous pocket where the pulse generator is implanted.
When an electrical pulse, or sequence of pulses, is applied to a selected electrode, or combination of electrodes, the patient typically experiences a “paresthesia” (usually manifest as a mild tingling sensation) that is therapeutic, i.e., that relieves the pain, or other discomfort, the patient is experiencing, or that otherwise aids the patient in some useful way.
Spinal cord and other stimulation systems are known in the art. For example, in U.S. Pat. No. 3,646,940, there is disclosed an implantable electronic stimulator that provides timed sequenced electrical impulses to a plurality of electrodes so that only one electrode has a voltage applied to it at any given time. Thus, the electrical stimuli provided by the apparatus taught in the '940 patent comprise sequential, or non-overlapping, stimuli.
In U.S. Pat. No. 3,724,467, an electrode implant is disclosed for the neuro-stimulation of the spinal cord. A relatively thin and flexible strip of physiologically inert plastic is provided with a plurality of electrodes formed thereon. The electrodes are connected by leads to an RF receiver, which is also implanted, and which is controlled by an external controller. The implanted RF receiver has no power storage means, and is coupled to the external controller in order for neuro-stimulation to occur.
In U.S. Pat. No. 3,822,708, another type of electrical spinal cord stimulating device is shown. The device has five aligned electrodes which are positioned longitudinally on the spinal cord and transversely to the nerves entering the spinal cord. Current pulses applied to the electrodes are said to block sensed intractable pain, while allowing passage of other sensations. The stimulation pulses applied to the electrodes are approximately 250 microseconds in width with a repetition rate of from 5 to 200 pulses per second. A patient-operable switch allows the patient to change which electrodes are activated, i.e., which electrodes receive the current stimulus, so that the area between the activated electrodes on the spinal cord can be adjusted, as required, to better block the pain.
Other representative patents that show spinal cord stimulation systems or electrodes include U.S. Pat. Nos. 4,338,945; 4,379,462; 4,519,403; 5,121,754; 5,417,719 and 5,501,703, incorporated herein by reference.
The '403 patent teaches a balloon lead and inflator. However, the '403 patent does not teach the use of a safety valve to release pressure that might build up, or otherwise be present, when such lead is used.
U.S. Pat. No. 5,733,322, also incorporated herein by reference, discloses a positive fixation percutaneous epidural neurostimulation lead that utilizes an extension that extends distally beyond the most distal electrode. The extension is held in place by contact with both the dura and spinal canal wall so that lateral lead migration of the electrodes is minimized. Other electrode fixation techniques are taught, e.g., in U.S. Pat. No. 4,418,697, which describes an adhesive (putty) to fixate electrodes to the skin; and in U.S. Pat. No. 4,282,886, which describes an adhesive adapted to attach an electrode to the epicardium. Both the '697 and the '886 patents are likewise incorporated herein by reference.
Disadvantageously, when a neural stimulation lead chronically or temporarily moves, the ramifications to the patient are multifold. For example, an SOS lead that moves up, down or rotates to the side of the spinal cord can result in therapy no longer being adequate to attain the desired paresthesia, thereby rendering the SOS system incapable of performing its intended function. On a temporary basis, the lead can move, which movement may thereafter require patient adjustment of the stimulation energy, e.g., to reduce the stimulation output or increase the stimulation output, and in some instances such adjustment of the stimulation energy may not be possible, thereby again rendering the SOS system ineffective for its intended purpose.
Thus, it is seen that maintaining the correct lead position is critical, and an undesirable movement of the lead can render the SOS, or other neural stimulation system, ineffective and useless. Moreover, as the correct lead position is maintained, appropriate safeguards should exist to prevent excessive compression of the spinal cord. What is needed are mechanisms built into the lead design that (1) acutely fixate the lead to its desired location, e.g., to the dura in the case of an SOS system, to thereby allow scare maturation to occur (which scare maturation will thereafter permanently maintain the lead in its desired location); or (2) permanently fixate the lead in its desired location from the onset of implantation; and (3) limit compression on the spinal cord.